1. Technical Field
The present invention relates to improved flexure devices as well as to the use of such devices in instrument stages capable of independent movement in each of two orthogonally/related dimensions. More particularly, the invention relates to an instrument stage having an output device form capable of independent xy motion in a single plane and which is virtually free of pitch, roll and yaw and of motion perpendicular to the plane of motion.
2. Discussion of the Prior Art
The flexure device of the present invention is an improvement over the flexure hinges described and illustrated in a publication by Paros, et al. entitled: "HOW TO DESIGN FLEXURE HINGES" which appeared in the Nov. 25, 1965 issue of MACHINE DESIGN magazine at pages 151-156, inclusive. The subject matter of that publication is expressly incorporated herein by reference in its entirety.
The flexure hinges described in the aforementioned Paros, et al. publication permit angular flexure in a member made of normally non-flexible material. The angular flexure is achieved by providing cut-outs or recesses from opposite edges of the member, which cut-outs or recesses are separated by a web-like section that is sufficiently thin to provide the desired angular flexure capability. The recesses may be of circular or rectangular cross-section and define a flexure pivot axis which extends transversely through the web. A two-axis flexure may be provided by using two pairs of such cut-outs or recesses, each pair being defined to a different pair of edges of the member. As described in the Paros et al. publication, the thinnest part of the web may be lapped down to a thickness of 500 micro inches.
There are applications for flexure devices which require the device to flex not only angularly but lengthwise. For example, in an instrument stage, it is often desirable to move a platform in each of the x and y dimensions independently in a single plane. More specifically, in measuring surface microtopography, in order to survey a surface area accurately, the scanning stage used to move the specimen surface under a fixed stylus must move in a true horizontal plane, and orthogonality of axis motion should require no corrective servo control. For example, referring to FIG. 6 of the accompanying drawings, it is desirable that the stage, diagrammatically represented by the reference numeral 10, be movable along the y-axis, for example, without any x-axis displacement. It has been suggested that flexure hinges 11 of the type disclosed by Paros, et al. be employed so that they may be pivoted through an angle to permit the desired y-axis displacement. However, as seen in FIG. 6, angular flexure alone of hinges 11 produces off-axis displacement x.sub.1 as well as the desired movement on-axis. Specifically, hinges 11 are unable to expand in length and therefore cannot accomodate the desired movement of the stage solely along the y-axis. Thus, the Paros, et al. flexure hinges cannot serve the intended function described hereinabove. This is unfortunate in view of the fact that such hinges are quite valuable where angular motion about a compliant axis is limited and zero friction and backlash are of paramount importance. Moreover, such hinges, compliant about the desired pivot axis, are substantially rigid about the cross-axis.
One could, of course, build a two-axis instrument stage using mechanical sliding joints, ball bearings, lubricants, etc. However, such expedients tend to be unreliable, have "stick-slip" friction, excessive bearing noise, require continuous calibration adjustment, and are not consistent with applications requiring a vacuum environment such as is present in a scanning electron microscope.